HDU5400——Arithmetic Sequence

http://acm.hdu.edu.cn/showproblem.php?pid=5400

/************************************************
* Author        :Powatr
* Created Time  :2015-8-18 13:00:59
* File Name     :1005.cpp
 ************************************************/

#include <cstdio>
#include <algorithm>
#include <iostream>
#include <sstream>
#include <cstring>
#include <cmath>
#include <string>
#include <vector>
#include <queue>
#include <deque>
#include <stack>
#include <list>
#include <map>
#include <set>
#include <bitset>
#include <cstdlib>
#include <ctime>
using namespace std;

#define lson l, mid, rt << 1
#define rson mid + 1, r, rt << 1 | 1
typedef long long ll;
const int MAXN = 1e5 + 10;
const int INF = 0x3f3f3f3f;
const int MOD = 1e9 + 7;

int a[MAXN];
int pre1[MAXN], pre2[MAXN];
int main(){
    int n, d1, d2;
    while(~scanf("%d%d%d", &n, &d1, &d2)){
        for(int i = 1; i <= n; i++)
            scanf("%d", &a[i]);
        memset(pre1, 0, sizeof(pre1));
        memset(pre2, 0, sizeof(pre2));
        for(int i = 1; i < n; i++){
            if(a[i+1] - a[i] == d1)
                pre1[i+1] = pre1[i] + 1;
        }
        for(int i = n; i >= 2; i--){
            if(a[i] - a[i-1] == d2)
                pre2[i-1] = pre2[i] + 1;
        }
        if(d1 == d2){
            int num = 1;
            ll ans = 0;
            for(int i = 1; i < n; i++){
                if(a[i+1] - a[i] == d1){
                    num++;
                }
                else{
                    ans += 1ll*num*(num+1)/2;
                    num = 1;
                }
            }
            ans += 1ll*num*(num+1)/2;
            printf("%I64d
", ans);
            continue;
        }
        ll ans = 0;
        
        for(int i = 1; i <= n; i++)
                ans += (1ll*(pre1[i]+1) * 1ll*(pre2[i]+1));
        printf("%I64d
", ans);
    }
    return 0;
}